Nature study reports 10% lower critical temperature and anomalous metal state in single-layer Bi-2201

August 12, 2026 at 05:00 AM2 min

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A study published in Nature reports that a single CuO2 plane in the cuprate Bi-2201 lowers the optimal superconducting transition temperature by about 10% compared with thicker samples. In the same monolayer specimens, finely controlled oxygenation reveals an anomalous metal state that emerges between the insulating and superconducting phases as temperature approaches zero. The findings push cuprate physics to the ultimate two-dimensional limit.

The Single-Layer Limit

The study isolates a single layer of Bi2Sr2CuO6+δ (Bi-2201), which contains only one CuO2 plane. Researchers report that this ultimate two-dimensional limit produces a robust dimensionality effect: the optimal superconducting transition temperature falls by approximately 10 percent. Earlier experiments on bilayer cuprates had shown that essential high-temperature superconductivity physics is contained in just two CuO2 planes. The new result extends that top-down approach to a single plane. The work appears in Nature.

Oxygen Tuning and Phase Diagram

Fine control of oxygenation in single-monolayer Bi-2201 specimens allowed the team to extend the material's phase diagram into uncharted territory. This tunability revealed an anomalous metal state that appears between the insulating and superconducting phases as the temperature approaches zero. The observation links oxygen doping to the emergence of a metallic regime that is not present in bulk samples. The study appears in Nature and includes datasets available from the corresponding authors.

Anomalous Scaling

Alongside the anomalous metal state, the authors report anomalous scaling behaviour with a divergent critical exponent. The exponent characterises the transition between the insulating and superconducting states in the single CuO2 plane. These findings illuminate the nature of the superconductor-to-insulator quantum phase transition in cuprates. The single-layer platform offers a new way to test competing theoretical descriptions of the transition.